Earth mount utility-scale photovoltaic array with edge portions resting on ground support area

ABSTRACT

An earth mount-enabled utility-scale solar photovoltaic array has plural rows of solar panels supported on the ground s to establish an earth orientation of the solar panels. Edge portions of the panels rest on a ground support area and provide mechanical support, and an end curb member abuts at least one edge of the arrangement. The panels are interconnected in at least one series-connected string extending in at least two rows so that the string has a total distance between terminal ends of the series connection less than a lengthwise dimension of the solar panels constituting the string, routed to reduce “home run” connections at the end of the string.

RELATED APPLICATIONS

The present Patent application claims priority to U.S. patentapplication Ser. No. 16/682,517, filed Nov. 13, 2019, pending, whichclaims priority to Provisional Patent Application No. 62/903,369, filedSep. 20, 2019, both of which are incorporated into this document by thisreference.

BACKGROUND Technical Field

The disclosed technology relates to mounting of solar panels using aterrestrial or ground-based mounting system.

Background Art

Solar panels, also called solar modules, are assemblies of multiplephotovoltaic (PV) cells hardwired together to form a single unit,typically as a rigid piece, although it is also possible to provideflexible solar panels. Groups of solar panels are aggregated into anarray. The panels are also wired together to form a string, which are inturn connected to a power receiving unit, typically an inverter or othercontroller which provides an initial power output. One or more solararrays form a solar plant.

A silicon-based photovoltaic (PV) module, also commonly referred to ascrystalline silicon (C_Si), is a packaged, connected assembly oftypically 6×12 photovoltaic solar cells. For utility scaleinstallations, the solar panels comprise a plurality of solar cellshardwired into a single unit, which is the module or panel. In a typicalapplication, the panel is made up of component solar cells. In the aboveexample of 6×12, this would be 72 solar cells, although this can varysignificantly according to design choice. The individual solar cells maybe fabricated in any convenient manner, and if desired can be separatelyfabricated and mounted onto a panel substrate or can be directlyfabricated onto the substrate. There are other types of PV moduletechnology in use today such as “thin film” and variations ofsilicon-based technology. Of the thin film, at least two moduletechnologies stand out. The first is CdTe (Cadmium Tellurium), alsoknown as CadTel. The second is known as CIGS or CIS (Copper, Indium,Gallium, Selenium or simply Copper, Indium, Selenium).

Several panels are connected to form an array in a procedure called“stringing”. The number of panels making up a string can vary, but in atypical application, this can be 17-29 panels depending on both theenvironmental condition as well as the rated voltage of the moduleselected (string voltage). The size of an array is limited by powertransmission limitations, including limiting maximum voltage and currentat the array. The panels within an array are connected in one or moreseries and one or more parallel strings. A series string is a set ofpanels which are series-connected to one another. This increases thepower output of the string without a corresponding increase in current,but results in an increase in voltage. Since it is necessary to limitthe maximum voltage output of the string as well as the maximum currentoutput of the array, the array is often divided into multiple strings ofa common voltage while summing the currents.

The number of panels in a string is given by way of non-limitingexample, as this is a function of design considerations relating topanel voltage and related circuit parameters of the strings and arrays.

The arrays are in turn connected to power conversion and powertransmission circuitry. This is accomplished by the internal connectionof the solar cells within a panel, followed by connections betweenpanels in an array, followed by connections to an inverter eitherdirectly or through wiring harnesses. The inverter is the first circuitproviding the output of the solar plant. The inverter is connected tofurther output circuitry, which is connected to transmission circuitry.The details can vary, for example for systems with local powerconnections, but in most solar power systems, the first connection forpower conversion, distribution and transmission is the inverter. Inother words, the strings are connected either directly or through wiringharness connections to the inverter.

The disclosed techniques seek to reduce the levelized cost of energy(LCOE) created by modern utility scale solar PV power plants. Theutility scale solar PV power plant is unique from the many other formsof solar power electricity production. Due to the nature of the size,energy cost, safety, regulations, and operating requirements of utilityscale power production, the components, hardware, design, constructionmeans and methods, operations and maintenance all have both specific andunique features which afford them the designation “utility scale”.

Since the inception of PV technology, the technology has been aninherently expensive solution for power production. The PV cellscontained within the heart of the solar modules have been both expensiveto manufacture and relatively inefficient. Over the past 40 years,significant strides have been made on all fronts of PV cell and modulemanufacturing and technology, which have brought their price down to apoint which has made the cost of solar based energy generation equal toand even less than all other forms of power generation in certaingeographical areas.

When the technology was in its infancy, significant development wasdirected to handling and positioning the PV cells and their largerassemblies called modules. This development focused on what is nowcommonly referred to as “dual axis tracking”. This concept seeks to keepthe PV cells at perpendicular to the sun's rays—throughout the day andthe year. This method sought to extract the maximum energy from thecells to offset the very expensive module cost.

As the price and efficiency of the cells and then modules improved, thecosts of dual axis trackers became prohibitive relative to the cost ofthe panels. This resulted in the development two supplementaltechnologies now known as “fixed title” racking and “single-axistracking”. Further developments included adaptation for these newersystems to roof-top mounting on home, office, commercial and industrialbuildings. Fixed title and single-axis tracking methods are oftencategorized as “ground mount” technologies which separate them from the“roof mount” technologies. The ground mount reference is simply thatthey are not associated with a building rather they are supported byfree-standing structures with their own foundations.

Safety and regulatory requirements are generally applied to bothsecluded solar PV power plants and roof-top systems but are differentfor utility scale solar photovoltaic power plants than for solarphotovoltaic installations which are not in a protected area, as will bedescribed. A utility scale PV power plant typically operates at 1500volts DC for the module. These modules are not allowed in applicationsother than utility scale due to the regulatory requirements on thevoltage (EMF). Specifically, exceeding 600 volts on the DC side placesthe system in a category which requires alternative safety, andoperating requirements on the system. Examples include requiring asecured fence surrounding the power plant which doesn't allow the publicwith unfettered access to the higher voltages as well as specifictraining requirements and certifications for individuals who will beaccessing the utility scale solar plant.

The operation of utility scale solar voltaic power plants isdistinguished by typical operation at EMF exceeding 600 volts. This isestablished by several different code requirements, including the (US.)National Electrical Code (NEC), the International ElectrotechnicalCommission [3] (IEC, or Commission Electrotechnique Internationale), andits affiliates. Electrical connections between enclosures exceeding 600volts are required to be secured in an enclosure such as a room orfenced area which is restricted to trained or qualified personnel. Forthe purposes of this disclosure, such an enclosure will be described asa “protected area”. A non-limiting example of such a “protected area” isreferenced in NEC Article 110, Part C, which provides the generalrequirements for over 600-volt applications. There can be variations inthe voltage, as it is possible to design arrays that can safely operateat higher voltages in unprotected environments.

These distinctions just two examples of what separate utility scalesolar PV power plants from other approaches such as “solar roads”, or“personal use solar power devices”.

As for the continued push to reduce the price of energy from the powerplant, for reference, a utility scale solar plant can make electricityin the Southwestern US at $0.040/kWh as of the beginning 2019. With thesame technology in the PV cell's—other than the voltage, a rooftopmounted system will average out to roughly $0.12/kWhr. This is a 3×difference in energy cost using what is essentially the same PV celltechnology. The reasons for this drastic reduction in price go farbeyond the cell and the module, and in many cases are only allowed tohappen inside the utility scale plant.

Solar panels, when deployed, for example in large solar farms, aretypically mounted on racks with the racks orienting the panels towardthe sun. In the case of gimballed racks, called trackers, the panel ispivoted to face the sun throughout the day, with some systems alsoaccounting for solar elevation or otherwise account for the effect ofthe sun's analemma. The advantages of fixed racking solar panels and oftracking are of course to increase efficiency, both in establishing analignment normal to the sunlight and to utilize the physical area of thesolar cells more efficiently.

A fixed title rack system typically is positioned at −25° fromhorizontal, with the angle dependent on various factors including thelatitude of the installation site. If a panel is mounted 25° normal tothe sunlight, it will convert approximately the same percentage ofimpinging light, but the amount of impinging light will be the cosine ofthe angle from normal. Taking the example of 25°, the impinging light isapproximately 90% that of a normal alignment, with some additional lossfrom the fact that the alignment of the solar cells is at an angle tosolar light impingement. A tracker will generate 8%-11% more energy thancan be expected from fixed rack-mounted panels depending upon geographyand array configuration. If the cost of solar panels is relatively high,this loss from misalignment is significant, but as costs of solar panelsdecreases, the costs resulting from inefficient alignment decreases toan extent that it may be more cost-effective to increase the area of thepanel and forego the expense of racking or tracking.

Off the ground, there is no need to sustain ground-caused damage. Moregenerally, the nature of solar cells is such that they are generallywaterproof and durable. As an example, it is common for solar modules tobe tested and certified to withstand hail of up to 25 mm (one inch)falling at 23 m/sec. While it is possible to clean solar panels, as apractical matter, racked solar panels are not cleaned because theexpense is not justified by expected energy loss resulting from dirt anddust accumulation. As an example, in Southern California, estimatedenergy loss from dirt and dust is 6%/year, but if the panels werecleaned, the loss would approximate 1%/year.

One consideration in mounting solar panels on racks or trackers is thealbedo effect, resulting from sunlight reflecting from the ground,resulting in back side heating. This issue is addressed in various ways,the most common of which is coating the back side of the solar panelswith a white coating. A common coating for this purpose is a whitepigmented Tedlar® PVF, sold by El duPont de Neumours, of Wilmington,Del. The Tedlar® offers protection, but when pigmented white, reflectsmost of the back side light. A disadvantage is that, as a white coating,the white pigmented Tedlar® tends to retard heat discharge through theback side.

The voltage output of solar arrays is constrained. Conceptually, a solararray, or for that matter a portion of an entire solar plant, could beseries-wired to provide electrical power transmission voltage. Inaddition, for a need to segment a solar plant for redundancy,maintenance and to avoid arcing to the ground, solar panels are voltagelimited by their construction due to the potential of arcing through theglass and backing. In typical configurations, the array output voltage(series voltage of the panels in each string) is 1500 volts, with lowervoltages such as 600 volts for residential applications and otherapplications where untrained personnel are likely to be present.Therefore, conventionally, solar arrays are limited in voltage. To limitthe voltage, panels are arranged in groups called strings, which are inturn connected to the inverter through harnesses. It has been necessaryto provide harnessing arrangements due to the physical arrangement ofthe strings on the trackers or racks. In a typical tracker system, threesets of strings are used on a single tracker assembly. To connect thosestrings to the inverter, harnesses of varying configurations are used,although this number can change according to the length of the rack andother considerations.

The harnesses themselves are a significant cost factor. Since the systemis voltage-limited, the total power output of the plant translates tosubstantial wiring costs for harness systems. Similarly, power lossesthrough the wiring harness translates to additional costs. Therefore, itis desired to provide a configuration which reduces the length of cableruns in connection harnesses.

One wiring harness configuration used with racked modules is called“skip stringing” or “leapfrog wiring”. In skip stringing, wiringharnesses bypass alternate panels to provide efficient wiring bylimiting cabling to approximately the distance between alternatingmodules. The ability to achieve connections extending over a longerdistance without a proportional increase in cabling allows positive andnegative connections to be placed closer to the inverter, reducing theamount of harness conductors needed to connect to the inverter. Sincethe panels are alternately connected, the alternate panels within thesame physical row can provide a return circuit, thereby reducing thedistance between an end panel and the inverter. Ideally, one positive ornegative pole connection for connecting the string to the inverter isonly one panel away from the other pole connection to the inverter. Thisreduces the length of the “home run” wire but requires that each linkskip alternate panels to return along the same row.

While it would be possible to string panels across two or more rows,doing so would result in shortening of the rows, which increases costs.Skip stringing wiring is used because, by skipping adjacent panels, thelength of a given string is maintained while providing for a returnconnection along the same row. This effectively doubles the length of astring over the length that would exist if the string were extendedacross two rows.

This system of stringing accommodates the polarities of the panels;however, this technique still requires wiring harnesses in theconnection. In addition, these techniques still require additionalharnesses to connect between the respective ends of the strings and theinverter. Since adjacent rows of panels are separated by a spacecorresponding to the cast shadow of racked panels, it becomesimpractical to string panels across rows.

Another issue involving rack- or tracker-mounted solar panels is theeffect of wind. High wind forces, which in certain geographies reachhurricane force strength, often preclude the construction of solar powerplants in those regions, or significantly increase the expense of doingso. In addition, the modules themselves are easily damaged by high windsrequiring significant repair and replacement expenditures. In additionto obvious damage resulting from the direct forces of wind, the negativeeffects of cyclic loading can result in “microcracking”. This“micro-cracking” damage occurs over time causing accelerated degradationrates of the module cells. This micro-cracking has become a seriousissue for the industry influencing long-term module warranties.

Another issue involving racked- or tracker-mounted solar panels is theeffect of environmental corrosion due to corrosive soils and corrosiveair such as salt spray. For example, typical power plants use drivensteel piles which are sized as small as possible to counter the effectsof wind loading on the overall structure. The design of the piles mustconsider the corrosion of the steel or other materials, and still beable to last for 25 years. The more corrosive the soil, the thicker theposts will be designed and used as sacrificial steel to ensure the25-year life. Similar issues exist for geographies near the oceans wheresalt spray environments exist.

A membrane mounting system for solar panels is described in USProvisional Application No. 2013/0056595 to Tomlinson, which shows amounting system in which a plurality of standoff mounts is secured to asubstrate or membrane in a parallel grid system. Mounting rails aresecured onto the standoff mounts, and attachment rails are eithersecured to opposing side edges of the panels, incorporated into thepanels, or incorporated into a supporting carrier for the panels.

SUMMARY

An earth mount enabled utility scale solar photovoltaic array iscomprised of a plurality of solar panels supported on the ground toestablish an earth orientation of the solar panels and positioned in aclosely adjacent arrangement or an abutting arrangement of plural rowsof the solar panels. The solar panels are supported on the ground atpanel edge portions, through an interstitial layer buffering theplurality of solar panels from the ground, to provide said support ofthe solar panels by the ground through the interstitial layer.

The solar panels are interconnected in at least one series-connectedstring, with the string extending along adjacent or closely adjacentsolar panels along at least two rows so that the string has a distancebetween terminal ends of the series connection less than a lengthwisedimension of the solar panels constituting the string. Theinterconnection comprises wiring connections engaging terminalconnections on the plurality of photovoltaic panels in theseries-connected string, the wiring connections arranged to connectadjacent panels in an arrangement utilizing at least two rows of panelsin the series-connected string connection, in which the string uses saidat least two rows to route the connections, The wiring connections arearranged so that a string starting with a first end termination extendsalong a direction of said at least two rows and returns along anopposite direction of said at least two rows, which reduces oreliminates “home run” connections at the end of the string.

The earth orientation reduces the cost of the photovoltaic array byeliminating costs associated with providing and installing elevatedsupports for the solar panels. The earth orientation also provides aflat orientation that permits cleaning with automated horizontal surfacecleaning equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a corner bracket used forattachment to a solar panel.

FIG. 2 depicts corner bracket 101 attached to solar panel.

FIGS. 3A-3D are schematic diagrams showing solar panels connected usingindividual corner brackets and a hold-down clamp. FIG. 3A shows ahold-down clamp. FIG. 3B shows the clamp engaging the corner brackets.FIG. 3C shows the clamp anchored and FIG. 3D is a top view.

FIG. 4 is a cross-sectional view of the clamping arrangement of FIGS.1-3.

FIGS. 5A and 5B are schematic diagrams showing a configuration of cornerbrackets, in which horizontal support is used to secure panels. FIG. 5Ashows a configuration for a clamp. FIG. 5B shows a configuration inwhich a bracket extends in a straight line connecting two modules.

FIGS. 6A and 6B are schematic diagrams showing a solar panel with itsedge frame resting on the ground. FIG. 6A shows a furrow placement. FIG.6B shows an end stop or curb member positioned at the edge of an array.

FIGS. 7A-7F are schematic diagrams showing configuration of cornerbrackets, in which a single disk supports four panels at corners of thepanels.

FIG. 7A is a perspective view of the corner bracket supporting fourpanels, with the panels in cut-away view. FIG. 7B shows the arrangementof the corner bracket.

FIG. 7C shows a bottom support. FIG. 7D shows a cross-section of thecorner bracket with a cinch pin. FIG. 7E shows the corner bracket andcinch pin gripping an anchor cable. FIG. 7F shows the corner bracketwith the cinch pin securing panels.

FIGS. 8A-8C are schematic diagrams showing configuration of a springclip arrangement used to link panels with a minimal gap between panels.FIG. 8A shows the spring clip in profile. FIG. 8B shows the spring clipin an elevation view.

FIG. 8C shows the spring clip engaging one solar panel.

FIGS. 9A and 9B are schematic diagrams showing the spring clip of FIGS.8A-8C gripping panels. FIG. 9A shows two adjacent panels held by aspring clip. FIG. 9B shows the gripping arrangement of the spring clip.

FIGS. 10A and 10B are schematic diagrams showing a wiring connectionlayout for adjacent solar panels.

FIG. 11 is a graphic diagram showing a sample output for a single clearsky day of the operation of a solar power plant. The horizontal axisrepresents time. The vertical axis on the left represents the availablesunlight, or “solar insolation”. The vertical axis on the rightindicates the power output of the power plant.

FIGS. 12A-12D are schematic diagrams showing a layout of a solar arrayfor a commercial solar power plant. FIG. 12A shows a partial stringarray of three strings of panels arranged in six rows. FIG. 12B expands12A to show a string array comprising 18 strings with a string inverterdepicted in the center. FIG. 12C further expands 12B to show 6 stringarrays further co-located to one another. FIG. 12D further expands 12Cto show a complete solar array.

DETAILED DESCRIPTION Overview

The disclosed technology provides a technique for generating electricityusing either commercially available, utility scale, solar PV (e.g., CSi,CdTe, CIGS, CIS) modules, or new and novel adaptations of commerciallyavailable, utility scale, solar PV modules, or new module technologies,a plurality of which are mounted in such a way as to be both in directcontact with the earth's surface and parallel to the same. Thisestablishes an earth orientation of the solar PV modules, asdistinguished from a solar orientation, although contouring of the soiland other mounting considerations will consider the angle of the sun.

The modules are placed in a grid pattern both edge to edge and end toend as if tiles on the floor of a house. The “utility scale” nature ofthe modules limits the application of said system to voltages exceeding600 volts DC which ensures the system is placed “behind the fence”whereby limiting access to trained professionals. There can bevariations in the threshold voltage, as it is possible to design arraysthat can safely operate at higher voltages in unprotected environments,a non-limiting example being 800-volt arrays for unprotected areas. Themethod of attachment of the modules to one another or to the earth isnot limited by this application. This arrangement of modulessubstantially reduces wind loading effects of the modules. Thearrangement of the modules electrically is in such a way as to allow forboth series and parallel connections, and eliminates, but does notpreclude the need for discrete wiring harnesses and harness supportingmeans used by traditional utility scale solar plant PV power plantsystems. This arrangement of modules provides for significant advantageswith the use of commercially available string/micro inverters but doesnot preclude the use of industry standard central inverters or alternatepower conversion and transmission technologies.

This arrangement of modules in conjunction with the use of activeelectrical protective devices such as ground fault interruption and arcfault interruption, fully eliminates the need and subsequent use ofelectrical grounding and bonding of the modules to the structure forpurposes of personal protection per code compliance. In contrast, thesedevices, when used in conjunction with conductive module supportstructures do not meet the protection levels necessary for codecompliance, and thusly require the use of bonding and grounding of themodules.

This arrangement of modules fully eliminates the need and subsequent useof steel and steel structures in the power plant thereby reducing and/oreliminating the natural weathering effects of corrosion while enhancinglife expectancy of the power plant from a minimum requirement of 25years to greater than 40 years. This system does not preclude the use ofsteel, coated or otherwise for site-specific applications.

The arrangement of modules allows for both commercially available andnew techniques for module cleaning and/or dust removal from the modulessurface, increasing the effective energy production rate of the modules.

The arrangement of modules and disclosed technology significantly reducethe negative effects of high wind forces on the modules. These windforces, which in certain geographies reach hurricane force strength,often preclude the construction of solar power plants in those regions,or significantly increase the expense of doing so. In addition, themodules themselves are easily damaged by high winds requiringsignificant repair and replacement expenditures. By removing the modulesfrom the direct forces of wind, the negative effects of cyclic loading,the “micro-cracking” is effectively eliminated.

The disclosed technology allows for both commercially available and newor novel methods for module cooling from the backside of the modules'surface including evaporative cooling, alternate high emissivitycoatings, the addition of “air vents” on the edge of the module frame,the addition of various enhanced heat transfer materials and or methods,thereby increasing the effective energy production rate of the modules.The positioning of the modules on the ground results in avoidingindirect sunlight and heat from ground exposed to sunlight from heatingthe backsides of the modules. As a result, rather than being a source ofadditional heat, the ground beneath the modules becomes more of a heatsink. To take further advantage of this, the modules are coated on thebackside with a dark or heat transmitting coating to promote radiantheat transfer to the ground or airspace beneath the modules.

The disclosed technology increases the power density per acre of land.The quantity of acres used per unit of power production is reduced bymore than 50% from traditional utility scale solar plant PV powerplants.

The disclosed technology allows the PV array to follow the existingcontour of the land whereby the need for land preparation such as massgrading, plowing, tilling, cutting, and filling as is typically neededfor utility scale solar plant PV power plants can be significantlyreduced and even eliminated.

The disclosed technology inherently results in an effective decrease inannual module performance yield as measured in kWhrs per kWp as comparedto traditional solar PV power plant systems because of not beingoriented to the sun as are the trackers and racks. While the energyperformance is significantly reduced, the reductions in electricallosses due to wiring, energy losses due to module cleaning, costsmaterials and construction, construction schedule and risk result in anoverall reduction in produced energy price (LCOE) of greater than 10%over current technologies.

The disclosed technology provides a system for a solar PV moduledirectly mounted to the earth. In one non-limiting configuration, abracket assembly utilizes the module frame as the structural supportsystem by securing the four corners of the solar PV module framedirectly to the earth leaving no air gap between the earth, framecorners, and bracket assembly. Earth mounting with no air gap reduceswind loading and uplift forces, and eliminates shading from panel topanel, has zero or minimal row spacing requirement, and increases theground coverage ratio. This earth mounted PV system orients the PVpanels parallel to existing topography and the solar panel arrays can bepositioned at any azimuth angle.

Solar panels, sometimes called solar modules, are configured as tilessuitable for installation directly on the earth and are configured totake advantage of the cooling and heat sinking effects of the earth. Inplacing the panels, attachment brackets may be used. The panels aresnapped into or otherwise secured to the attachment brackets, retaininga solar array on the ground or near the ground. The ground placementallows a low-cost configuration in that it avoids the requirements formounting the panels on racks and avoids shadows and the consequentialneed for spacing between rows.

Since the panels are not mounted on racks, the requirements for windtolerance are significantly reduced. This also reduces the need toanchor the panels because there are no racks to mount, and since thepanels are on the ground, there is substantially less lifting due towind conditions.

The mounting may use attachment brackets which connect adjacent panelstogether. While it is possible to anchor the brackets to the ground, theanchoring requirements, meaning anchoring force, is greatly reducedbecause the panels are not supported above-ground in the wind at anangle to the horizontal. Instead, the panels rest substantially flat onthe ground or near the ground.

The brackets secure the panels to each other and maintain a fixedpositioning of the panels to stabilize the panels in a desired position.Anchor stakes augment this stability but need only secure the panelsagainst forces experienced when laid flat on the ground, which issubstantially lower than the force incurred in rack-mounted or trackermounted configurations.

The lack of shadows is in part the effect of the panels not beingtilted. This results in reduced power conversion as compared to panelsoriented toward the sun, but if the total costs of the array withoutracks compares favorably with the loss of output from flat placement,flat placement can be cost-effective.

The lack of shadowing between adjacent rows of panels falls into thiseconomic balance. The reason there is no shadowing is that the shadowingis created by the racking, and more specifically, from the angledpositioning of the racked panels. Since racking is not used, there is noshadowing, which allows configurations which close the gaps betweensequential rows. Elimination of the gaps establishes a two-dimensionalconnection array, meaning closely adjacent panels extend in a row-wisedirection as well as across sequential rows because sequential rows arealso adjacently positioned. In other words, gaps between sequentialpanels from row-to-row closely approximate gaps between sequentialpanels along the rows.

This adjacent positioning allows wiring connections or harnesses to takeadvantage of the adjacent relationships across two or more rows, therebyreducing the need for harness connections. In a particular arrangement,“home run” harness connections, commonly referred to as “whips”, aresignificantly reduced because adjacent rows can be connected without“skip stringing” or “leapfrog wiring”. In an alternate arrangement,sequential connections can be made with “next” panels in adjacent rows,thereby reducing the length of connections required for “skip stringing”or “leapfrog wiring”.

The elimination of racking affords an additional advantage when it comesto harnessing. Since there are no racks, the need to extend the lengthof racks is reduced to the need to limit the voltages of the strings,without consideration of the costs of the racks, or in the case oftrackers, the cost of tracker drive mechanisms. This, in turn, allowsthe strings to terminate at both ends of the strings close to theinverters. In this respect, having multiple strings terminate closetogether allows inverters to be positioned close to the end terminationsof the strings.

Mounting System

FIG. 1 is a schematic diagram showing a corner bracket 101 used forattachment to a solar panel. Depicted are flat body 111, inner panelattachment flange 112 outer panel attachment flange 113 and linkingflange 114. Inner and outer attachment flanges 112, 113 are formed tomate with an outer frame of a solar panel (201, FIG. 2). Outer panelattachment flange 113 is in a middle position because linking flange 114is intended for attachment outside of outer attachment flange 113.

Also depicted in FIG. 1 is frame grip 122, which is depicted as anangled or wedge portion of inner attachment flange 112. It is noted thatthe configuration of frame grip 122 is dependent on the physicalconfiguration of the solar panel's frame to which corner bracket 101mates.

FIG. 2 depicts corner bracket 101 attached to solar panel 201.

FIGS. 3A-3D are schematic diagrams showing solar panels 201 connectedusing individual corner brackets 101 and a hold-down clamp 301.Hold-down clamp 301 is used to link corner brackets 101, with clampflanges 314 on clamp 301 engaging linking flanges 114 on brackets 101.Clamp flanges 314 may also closely fit against outer attachment flanges113 for added stability, according to design choice. Also depicted isanchor bolt or pin 321 (FIG. 3C), which is used to secure hold-downclamp 301 to the ground or other supporting surface. Anchor bolt or pin321 is given as a non-limiting example, as any suitable anchoringmechanism can be used, provided corner brackets 101, hold-down clamp 301or another part can be secured to the anchoring mechanism.

A cross-section of the arrangement is depicted in FIG. 4. While adjacentcorner brackets 101, 101 are depicted as abutting, in the depictedarrangement, corner brackets 101, and hence panels 201 have lateralplay, as the primary function of corner brackets 101 and hold-down clamp301 is to retain panels 201 in place on the ground (verticalpositioning), with lateral movement inherently limited. So long as theconnecting cables or “strings” can tolerate the implied variations, thepositional tolerance would not affect the assembly. Other physicalvariations can be employed, so long as the clamping and hold-downfunctions are accomplished.

FIGS. 5A and 5B are schematic diagrams showing a configuration of cornerbrackets, in which horizontal support is used to secure panels. FIG. 5Ashows a configuration for a clamp 501 in which top and bottom cornerflanges 511, 512 are used. FIG. 5B shows a configuration in which abracket 531 extends in a straight line connecting two modules 201. Byusing interlocking links, opposing brackets 501-501 can be lockedtogether, and secured by the weight of the panels 201, with or withoutthe use of anchor bolts or pins 321 (FIG. 3C) or another suitableanchoring device.

In addition to simpler mounting, the flat mounting system makes somemaintenance tasks easier. By way of non-limiting example, cleaningequipment can be operated across the tops of the panels, as will bedescribed.

Furrow Mounting

The earth-oriented mounting lends to directly placing the panels on theground without the use of corner brackets or other external bracing. Inthe case of solar panels with frames, the frame can be rested on theground, which, in turn, provides mechanical support for the panels.FIGS. 6A and 6B are schematic diagrams showing a solar panel 601 withits edge frame 611 resting on the ground.

Referring to FIG. 6A, the ground is prepared by generally smoothing theground to desired contours for the panels 601. Furrows 621 are dug bymechanical means, and the panels 601 are placed on the ground with theiredge frames 611 resting against the sides of furrows 621. Furrows 621serve to positionally stabilize the panels 601 and provide themechanical support for the panels 601. While it is possible for thepanels 601 to directly rest on the ground on parts of the panels 601other than the edge frames 611, the support by the frames 611 reducesmechanical force applied to the active parts of the panels 601 andleaves additional room for electrical connections. Thus, the furrows 621are formed as grooves, depressions or channels dug into the ground toreceive the edge frames 611.

While smoothing and prior ground preparation is described, it ispossible in some circumstances to avoid some of the grading andcontouring steps. It is also possible that some ground conditions allowdirect placement of the edge frames 611 with the edge frames 611securing the panels 601 to the ground without a specially preparedfurrow. The smoothing facilitates orienting the panels substantiallyparallel to the ground.

FIG. 6B shows an end stop or curb member 635 positioned at the edge ofan array. Curb 635 can be made of any convenient low-cost material andserves to retard movement of the panels along the edges of the array.Since adjacent panels within the array abut one another or are otherwisenear each other, the only place for lateral movement would be along theedges of the array, which is prevented by curb 635. Curb 635 alsodirects surface water over the tops of the panels 601, which reduces thepotential for washout of the soil and lifting of the panels 601 causedby surface water. Additionally, causing surface water to flow over thetops of panels 601 has some benefit in keeping the panels 601 clean.These advantages are also useful in installations in which cornerbrackets or other brackets are used to support solar panels.

The depiction of FIG. 6B shows water flow on the upslope side of thearray, in which water may have sufficient velocity to flow upward overto top, as indicated by the arrows. Water that pools at curb 635 wouldbe able to flow laterally parallel to curb 635 or percolate into theground.

Furrows 621 are given by way of non-limiting example. In manyinstallations, it is possible to directly support the panels 601 or theedge frames 611 directly on the ground without digging furrows. In somesoil conditions, the edge frames 611 will sink into the soil, whereas inother conditions, the edge frames 611 will remain substantially at thetop surface of the ground. It is further expected that the panels 601will rest against the ground without the use of the edge frames 611,either because the edge frames 611 can sink below a level at which thepanels will rest on the ground, or in cases in which panels areconstructed without edge frames.

Alternate Mounting Systems

FIGS. 7A-7F are schematic diagrams showing configuration of cornerbrackets, in which a single disk supports four panels at corners of thepanels.

FIG. 7A is a perspective view of the corner bracket supporting fourpanels, with the panels in cut-away view. FIG. 7B shows the arrangementof the corner bracket. FIG. 7C shows a bottom support. FIG. 7D shows across-section of the corner bracket with a cinch pin. FIG. 7E shows thecorner bracket and cinch pin gripping an anchor cable. FIG. 7F shows thecorner bracket with the cinch pin securing panels.

The configuration of FIGS. 7A-7F allows simplified mounting, and furtherfacilitates the use of anchor cables. The anchor cable can be anyconvenient anchoring system, such as a cable anchoring system producedby American Earth Anchors of Franklin, Mass. (US), one variation beingthe Model 3ST60QV anchor system, which uses a pivoting spade attached towire rope. The wire rope is swaged or cinched by a swage fitting such asan American Earth Anchors Quickvice QV18 swage fitting (Quickvice is atrademark of American Earth Anchors). The anchor system sold by AmericanEarth Anchors is given by way of non-limiting example, as a wide varietyof convenient anchoring systems can be used.

Advantageously, since the panels are resting on the ground, they are notgenerally exposed to sufficient upward force to lift them upward.Therefore, the soil anchoring system need only provide intermittentanchoring support, for example when exposed to weather events resultingin strong winds.

FIGS. 8A-8C are schematic diagrams showing configuration of a springclip arrangement used to link panels with a minimal gap between panelsusing spring clip 801. FIG. 8A shows spring clip 801 in profile. FIG. 8Bshows spring clip 801 in an elevation view. FIG. 8C shows spring clip801 engaging one solar panel. Spring clip 801 comprises a flat sheet811, folded to outer frame support 813 (for the outer frame sides ofsolar panels), with raised retainer lips 814, and two inner framesupports 817 (for inner frame edges of the solar panels), with raisedretainer lips 818. As can be seen in FIG. 8C, solar panel 201 isretained with its outer frame resting against outer frame support 813and held down by retainer lip 814. The corresponding inner frame support817 is hidden from view in FIG. 8C. Stake holes 823 (FIGS. 8B and 8C)facilitate anchoring spring clip 810 to the ground, for example by useof an anchor stake or an alternate anchoring system such as theabove-mentioned cable anchoring system produced by American EarthAnchors.

FIGS. 9A and 9B are schematic diagrams showing the spring clip of FIGS.8A-8C gripping panels. FIG. 9A shows two adjacent panels 201 held byspring clip 801. FIG. 9B shows the gripping arrangement of spring clip801. As can be seen in FIG. 9A, the arrangement is such that adjacentsolar panels 201-201 fit closely together, which reduces the gap betweenthe adjacent solar panels and reduces the tendency of the solar panels201 to lift when exposed to strong winds.

To install solar panels 201 into spring clip, the panels are positionedin place and downward pressure is applied to cause the panels 201 tosnap into place.

It is further possible to restrain the panels by other techniques. Byway of non-limiting example, adjacent panels can be linked together.Other linkages include cables or rods routed through support edges ofthe panels. The cables or rods can extend across multiple panels oracross the length or width of the array,

Backside Cooling

A further advantage of mounting the modules on the ground or just abovethe ground is that cooling from the backside of the modules' surface iseasily accomplished. Cooling techniques can include, by way ofnon-limiting example, evaporative cooling, alternate high emissivitycoatings, the addition of “air vents” on the edge of the module frame,and the addition of various enhanced heat transfer materials and ormethods. The increased cooling, by reducing the operating temperature,increases the effective energy production rate of the modules. Thepositioning of the modules on the ground results in avoiding indirectsunlight and heat from ground exposed to sunlight from heating thebacksides of the modules. As a result, rather than being a source ofadditional heat, the ground beneath the modules becomes more of a heatsink. To take further advantage of this, the modules are coated on thebackside with a dark or heat transmitting coating to promote radiantheat transfer to the ground or airspace beneath the modules. By way ofnon-limiting example, the dark or heat transmitting coating is providedas black-pigmented Tedlar® PVF, sold by El duPont de Neumours, ofWilmington, Del., or a dark Tedlar® coating sold as “Tedlar® Charcoal”.

Ventilation of the backside can be accomplished by a variety oftechniques. By way of non-limiting example, outlet vents can connect toone or more vertical stacks to use convection to remove warm air.Alternatively, DC power can be used to operate fans either when power isproduced or when peak power is sensed. Inlet vents can use separatesupply tubing or louvers cut into edge frames of the modules.

Stringed Panels

FIGS. 10A and 10B are schematic diagrams showing a wiring connectionlayout for adjacent solar panels 201. FIG. 10A shows an array of threestrings of panels arranged of in six rows. FIG. 10B shows connectiondetails. Adjacent panels 301 within a row are series-connected. At oneend of the row, the series connection extends to the next row, and thenreturns to the starting end. The end connections are in turn connectedto inverter 1015. Inverter 1015 converts the power for downstream poweruse in the usual manner. While one inverter 1015 is shown, multipleinverters 1015 can be used, to place the inverter connection closer tothe terminal ends of the rows.

This arrangement limits the length of the series connection, and therebylimits output voltage of the array itself to permissible levels. Atypical voltage limit for a string of arrays is 1500 volts, although inresidential installations and other installations where non-qualifiedpersonnel are present are typically limited to lower voltages, such as600 volts. The arrangement conveniently limits the voltage to the seriesoutput by limiting the length of the respective strings (i.e., thenumber of panels connected in series).

The stringing technique works because, without racking or trackers, thelength of the rows can be made shorter. Additionally, since there is noseparate pathway between adjacent rows, running harnessing between rowsis less complicated. By way of non-limiting example, the length of therows can be several panels to produce half the maximum design voltage(to accommodate the return run). The individual panels are provided withterminal leads or pigtails, which are directly connected to each other.This arrangement eliminates the need to provide “home run” harnessconnections to link the end of a string of panels to an inverterconnection at the end of the row. The end-of-row connection must stillbe connected to the nearest inverter if the inverter is not situatedimmediately at the end of the row, but the intermediate connectionsrequired to extend a string to the end of a much longer row areeliminated. Additional reduction in harnessing connections can beachieved using individual inverters at the ends of the respective pairsof rows.

Power Output

FIG. 11 is a graphic diagram showing a sample output for a single clearsky day of the operation of a solar power plant. The horizontal axisrepresents time, specifically a sample of daylight hours from roughly 7a.m. to roughly 7 p.m., where “solar noon” is represented by the peak ofthe graph. The vertical axis on the left represents the availablesunlight, or “solar insolation” as measured in watts per meter squared(W/m2) or the typical amount of energy available from the sun during agiven day. The curve which peaks out at 1000 W/m2 is representative of atypical day of sunlight. The peak, as represented by “noon” is solarnoon, not to be confused with the 12 o'clock hour, which typicallyvaries from solar noon. The vertical axis on the right indicates the ACpower output of the power plant, as well as the DC power potential ofthe power plant, on common scales of MW, or megawatts. The actual ACpower output of the plant is represented by the two lower curves. Thecurve characterized by the double hump is a typical sample of a trackertype solar plant, with a maximum delivered power of 1 MW (in thisexample). The sharp dip in the tracker curve is emblematic of a cloudmoving across the power plant between the plant and the sun. The otherlower curve represents the earth-oriented power plant power curve, alsowith a maximum delivered power of 1 MW. The two dotted lines extendingabove the power curves represent the additional unused portion of DCpower available. The smaller of the two curves, which peaks out at 1.25is the tracker power plant, while the taller curve, peaking out at 1.45is the earth-oriented power plant.

The AC power output of the power plant is intentionally limited forpractical reasons, mostly related to grid capacity to absorb largeamounts of power during a small part of the day. Therefore, the AC poweroutput shows a flat peak at 1.00 MW on this graph. The excess power iseither not used or applied to alternative uses such as energy storage.If alternative energy storage is limited or not available, then it ispossible to use the additional energy to support the grid in volt-amperereactive units (vars, sometime given as VARs), or other power functionsother than direct increases in power output (MW). Alternatively, theexcess power con be purchased as surplus power by the grid utility ortransported across the grid for use at a remote location.

An economic advantage of the earth-oriented arrangement of the solarmodules results from the relative economics of the DC power generationcomponents as opposed to the total cost of operations of the powerplant. As depicted in FIG. 11, the two power curves have an arbitrarylimit of 1 MW. This limit is set by the utility company, to which thepower is sold. This limit is a function of the needs of the utilitycompany at the point of interconnection of the power plant and cannot beexceeded by contract nor design. An important point of note is that theavailable DC power from the earth-oriented power plant is greater thanthe available DC power from the tracker power plant as is depicted inFIG. 11. This fact is a result of the difference in power plant design,function, and economics. The earth-oriented power plant has more DCpower available because it has more modules in use for the same size AC.This is due to the elimination of the additional physical hardwarerequired to hold the modules in space as well as the amount of landrequired to house the quantity of modules mounted on racks sufficientlyspaced apart as to not shade one another. The earth-oriented plant hasan intrinsic advantage over the tracker and fixed title plant in that itcan contain more DC as a percentage of the design output whichtranslates to the AC size. The additional DC power in the power planthas intrinsic value when available. This is true for any solar plantsized with a DC:AC ratio greater than 1.0. Since it cannot be used todeliver real power to the grid (the delivery of which results inrevenues for the power plant owner), it is maintained as potentialpower, waiting to be dispatched when and if needed. There are multipleways this intrinsic value is captured and can bring value to the assetowner.

First, during periods of intermittent cloud cover, the clouds may onlycover portions of the power plant. The balance of the plant is availableto run full power. The potential power of the additional DC has theeffect of allowing the plant to ride through lower light conditions fromclouds while still delivering 100% of the AC power plant capacityallowed by the grid connection. If there is greater DC potential, thepower plant can ride through larger clouds, and slower moving cloudswithout going below 100% capacity. This effect is currently notcalculated in the industry as it is currently impossible to make thesemeasurements. As such, approximations are used. The accuracy of theseapproximations can only be determined by empirical means. What can besaid is that the additional DC potential will result in some amount ofbenefit that is greater than zero.

Second, the utility operator receiving real power from the power planthas developed the means to use the potential DC power to the benefit oftheir system. This benefit comes in the form supplemental voltage, andfrequency regulation of the grid by adjusting the power factor controlcapabilities of the connected set of inverters. Modem solar poweroperators have become aware of this benefit and are now selling thisportion of the available power in the form of vars to the utility. Theadditional DC potential of the earth-oriented plant brings additionalvars available to be sold as compared to a non-earth-oriented solarplant of the same AC power rating.

Third, as the use of solid-state batteries or other energy storage orconversion means have become more financially viable, the ability toconvert the potential DC power from the solar plant into potential DCenergy, stored in the storage means, allows for the direct transfer ofthe potential DC power into the sale of real energy to the grid at timeswhen the sun is not available or other valuable use of the energy. Theadditional DC potential of the earth-oriented plant brings additionalenergy potential available to be sold as compared to anon-earth-oriented solar plant of the same AC power rating.

Solar Plant Layout

FIGS. 12A-12D are schematic diagrams showing a layout of a solar arrayfor a commercial solar power plant. FIG. 12A shows a partial stringarray of three strings of panels arranged in six rows. FIG. 12B expands12A to show a string array comprising 18 strings with a string inverterdepicted in the center. The inverter I015 is connected to the stringsfor purposes of converting the DC power from the strings to AC power.FIG. 12C further expands 12B to show 6 string arrays further co-locatedto one another. FIG. 12D further expands 12C to show a complete solararray 1220 comprised of 18 string arrays, 18 string inverters, 324strings, and a single medium voltage transformer which receives powerfrom the six sets of three series-connected string inverters. A utilityscale solar power plant typically comprises one or more of these arrays.

Cleaning

The flat orientation of the panels also provides advantages as far ascleaning is concerned. Panels in a flat arrangement can easily becleaned by an automated warehouse street sweeper. Such cleaning devices,such as the FyBot ‘L’ (trademark of FyBots of Voisins-le-Bretonneux,France), a commercially available fully autonomous warehouse sweepingrobot, similar in operation to home-use robotic vacuum cleaners such asthe Roomba (trademark of iRobot Corporation), and the automated cleaningtechnique was tested with a Roomba 690-type cleaner. While cleaning ismore important for earth-oriented solar panels, the ability to uselow-cost automated cleaning allows frequent cleaning at significantlyless cost than would be incurred in if one were to institute a regimenfor cleaning rack-mounted arrays. The implementation of a low-costcleaning regimen on earth-oriented arrays results in soiling lossreductions from typically 6% for fixed title and 3.5% for trackers,non-cleaned, down to less than 1% for the cleaned earth-oriented array.

Referring again to FIGS. 12A-12D, to traverse gaps between the portionsof the arrays, bridges 1233 are provided to connect gaps within thearray to allow the automated warehouse street sweeper to automaticallytraverse the gaps. Similar bridges can be provided between arrays aswell, to allow the cleaning operation to continue automatically acrossmultiple arrays.

It will be understood that many additional changes in the details,materials, steps, and arrangement of parts, which have been hereindescribed and illustrated to explain the nature of the subject matter,may be made by those skilled in the art within the principle and scopeof the invention as expressed in the appended claims.

1. A method comprising providing a power plant having at least one arrayof PV modules by supporting modules in rows resting on the ground in anearth orientation, and providing a connection between proximate modules.2. The method of claim 1, wherein the connection vertically aligns themodule faces.
 3. The method of claim 2, wherein vertically aligns isaligned close enough to permit an autonomous cleaning robot to clean thearray.
 4. The method of claim 3 further comprising resting module edgeframes on a ground support area capable of supporting the edge frames byreceiving the edge frames of the modules.
 5. The method of claim 4,wherein supporting modules on the ground includes supporting modules onthe ground with module edge frames directly resting on the ground in anearth orientation.
 6. The method of claim 5, wherein the edge framesresting on the ground support area provides mechanical support for themodule.
 7. The method of claim 6, wherein edge portions the edge framesof the solar module rest on a ground support area capable of supportingthe edge portions frames by receiving edge frames of a plurality ofmodules to contact the ground.
 8. The method of claim 7, wherein themodules contact the ground without a mechanical support structurebetween the modules and the ground.
 9. The method of claim 8, whereinthe connection includes an inter-module connector.
 10. The method ofclaim 9, wherein the connection comprises a bracket or spring-cliparrangement.
 11. The method of claim 10, further comprising:interconnecting the modules in a series-connected string, wherein thestring extends between adjacent modules along at least two rows and thestring has terminal ends with a distance between ends less than alengthwise dimension of the string modules.
 12. The method of claim 11,wherein the string uses the rows to route the connections so that astring starting with a first end termination extends along a directionand returns along an opposite direction. The method of claim 12 furthercomprising operating the power plant.
 13. The method of claim 12,wherein operating the power plant comprises cleaning the array by usingan autonomous cleaning robot to clean the modules.
 14. The method ofclaim 13 further comprising operating the power plant.
 15. The method ofclaim 14, wherein operating the power plant comprises cleaning the arrayby using an autonomous cleaning robot to clean the modules.
 16. Themethod of claim 1, wherein the modules contact the ground without amechanical support structure between the modules and the ground.
 17. Themethod of claim 16, wherein the connection includes an inter-moduleconnector.
 18. The method of claim 17, wherein the connection comprisesa bracket or spring-clip arrangement.
 19. The method of claim 18,further comprising: interconnecting the modules in a series-connectedstring, wherein the string extends between adjacent modules along atleast two rows and the string has terminal ends with a distance betweenends less than a lengthwise dimension of the string modules.
 20. Themethod of claim 19, wherein the string uses the rows to route theconnections so that a string starting with a first end terminationextends along a direction and returns along an opposite direction. 21.The method of claim 20 further comprising operating the power plant. 22.The method of claim 21, wherein operating the power plant comprisescleaning the array by using an autonomous cleaning robot to clean themodules.